Quantitative Comparison Of Different Ultrasonic Testing Methods For Weld Crack In Alloy Steel

Crack is one of the most harmful defects in weld because it is easy to expand by external force.According to the theory of fracture mechanics,when the crack reaches the critical size,under the action of external load,instantaneous fracture is extremely easy to occur,causing a major safety accident.Ultrasonic testing is widely used in practical engineering because of its sensitivity to area defects,high accuracy in localization and quantification.Among them,the conventional ultrasonic detection represented by the pulse reflection method is the first to be applied.This method relies on the amplitude of defect echo to realize the localization and quantification of defects,so this method is greatly affected by human and has low accuracy of localization and quantification.At present,the method of Time difference Ultrasonic Diffraction(Time of Flight Diffraction,TOFD)and Phased Array Ultrasonic Testing technology(Phased Array Ultrasonic Testing,PAUT)gradually emerging,such as Ultrasonic Testing technology is applied to the engineering test,TOFD rely on acoustic Time difference defects and endpoint for quantitative research,has the advantages of high precision quantitative PAUT by computer generated delay law,to control the emission and receiving of different.Compared with the pulse reflection method,the detection signal to noise ratio is improved obviously.But the usability of different methods varies.In this paper,the artificial prefabricated cracks in alloy steel Q235 are compared and studied through simulation and experiment on the detection rate and quantitative detection accuracy of the defects of pulse echo method,TOFD and PAUT.The main research contents are as follows:(1)In the Q235 model of alloy steel with a thickness of 100 mm,9 cracks with a height of 3.0 mm were set with a gradient of 10 mm.Simulation results show that all cracks can be detected by three ultrasonic detection techniques.The quantitative error of the crack height in the pulse reflection method is about 1.00 mm,which is independent of the buried depth of the crack.TOFD has the highest quantitative accuracy and the detection error is less than 0.10 mm.The quantitative detection error of PAUT increases with the increase of crack depth,up to 0.85 mm.Experimental verification was carried out for cracks with a depth of 10 mm,50 mm,90 mm and a height of 3.0 mm.The experimental results of TOFD and PAUT were consistent with the simulation results.The experimental quantitative accuracy of pulse reflection method is low due to the influence of crack morphology.(2)In the model with a thickness of 30 mm,5 cracks with a height of 1.0 mm,2.0 mm,3.0 mm,4.0 mm and 5.0 mm were set in the depth of 15 mm.Simulation results show that the pulse reflection method can not detect cracks of 1.00 mm,and all preset cracks can be detected by TOFD and PAUT.The quantitative error of pulse reflection method increases with the increase of crack height.TOFD quantitative error is less than 0.10 mm,and the quantitative accuracy is the highest.The quantitative error of PAUT decreases with the increase of crack height.2.0 mm,3.0 mm and 5.0 mm height cracks were selected for experimental verification,and the results of TOFD and PAUT were consistent with the simulation results.The experimental quantitative error of pulse reflection method decreases as the crack height increases.(3)Within the thickness of 30 mm model,depth of 15 mm and 60 ° ~ 60 ° interval,set up 9 to 15° gradient,inclined crack length is 3.0 mm.Simulation results show that all preset cracks can be detected by three ultrasonic detection techniques.The length quantitative error of pulse reflection method fluctuates within the range of 0.15-1.29 mm.The TOFD quantitative error increases with the crack inclination Angle.The quantitative accuracy of positive-oriented cracks on PAUT is higher than that of negative-oriented cracks.The quantitative error is less than 0.31 mm.Selection of plus or minus 30°,60°,plus or minus 0° crack experiment validation,TOFD with PAUT results and simulation results have good consistency;The experimental quantitative accuracy of pulse reflection method is low due to the influence of crack morphology.A comparative study shows that for vertical cracks,when the workpiece thickness is less than 50 mm,the quantitative accuracy of the selected TOFD is equivalent to that of PAUT,but when the crack size is less than 2.0 mm,the quantitative error of PAUT will increase.PAUT is the best choice for quantitative study of inclined crack.